Dic:// blue-sky

─ 1. a) Not limited by conventional notions of what is practical or feasible; imaginative or visionary.

• "Proponents of blue-sky thinking often cite the Wright brothers as validation." (David Colman)

─  . b) Unrealistic or impractical.

• "[The author] shows what is testable physics, what is philosophy's domain, and what is blue-sky nonsense." (Ann Finkbeiner)

─ 2. or blue-skied. Having a cloudless sky; clear: a blue-sky day.

─ 3. intr.v. To hold or express unrealistic or impractical views, esp in estimating something.

─. n (modifier) of or denoting theoretical research without regard to any future application of its result: a blue-sky project.

─. v. To theorize (about something that may not lead to any practical application)

....... American Heritage 5th edn 2016, Collins